This disclosure relates generally to circuit fabrication, and in particular but not exclusively, relates to a method of fabrication to sharpen corners used in Y-branches, such as those in integrated optical components, photonic crystal devices, and other micro-devices.
Integrated optical devices, such as those formed on a planar lightwave circuit chip, typically include optical components in the form of optical waveguides. In fact, optical waveguides are often the fundamental component of all integrated optical devices. The optical waveguides operate to direct light signals from one location to another, and often branch out or xe2x80x9csplitxe2x80x9d at various locations to allow the light signals to propagate to several different locations. A xe2x80x9cY-branchxe2x80x9d splitter configuration for an optical waveguide is a common configuration, although other configurations are also possible.
Because of the large size of a wafer having integrated optical devices (e.g., a large field size), contact lithography techniques are often used to manufacture optical waveguides. Through the use of lithographic patterning and etching, multiple optical waveguides (including their Y-branches) can be formed on a semiconductor chip.
However, contact lithography and other large-field lithography techniques produce non-optimal rounded corners or edges at the Y-branch. That is, their large exposure causes their resolution to suffer, thereby making sharp corners difficult to create. The rounded corners that result from poor resolution adversely affect efficiency and performance of the integrated optical device and the overall performance of the optical network. Specifically, the rounded corners present a large profile for light signals incident at the splitter location. This causes the incident power on the Y-branch to become non-guided or scattered, and therefore lost in the device.
In certain applications, high-resolution steppers and scanners (e.g., another type of lithography technique) are available. However, these instruments are impractical for an integrated optical device application due to their limited field size. Furthermore, optical performance considerations preclude the xe2x80x9cstitching togetherxe2x80x9d of multiple small-sized fields that have been formed using high-resolution steppers and scanners. Moreover, due to the wave-nature of light used in lithographic methods and due to the surface tension of the photoresist during the expose and development process, the resulting edges are rounded, which limits the optical performance of certain devices.